It is generally known that high optical quality, transparent plastic sheets having enhanced solar control properties may be used alone or in combination with other materials, e.g., glass, to prepare solar load reducing automotive and architectural glazings. A particularly useful combination comprises well-known asymmetrical laminated glazings, wherein a plastic sheet having enhanced solar control properties is laminated to a monolithic or multi-layered glass and/or plastic support. Such a combination would impart weight reduction and safety properties to an automotive or architectural glazing, in comparison to the all-glass construction of conventional glazings.
Enhanced solar control glazings are currently used in several areas where one objective is to manage internal heat loads, by reflecting a portion of the solar spectrum which causes heating (i.e., infrared radiation) while maximizing transmission of the visible light portion of the solar spectrum. Such technology has been employed, for example, in commercial and residential glazings, and more recently in automotive glazings.
It is also known that the solar control properties of glazings may be enhanced by conventional coating techniques such as, for example, vacuum deposition or plasma-enhanced chemical vapor deposition, wherein metal or dielectric films are placed on the surface of the glazing. For example, transparent dielectric layers of fluorine-doped tin oxide or indium oxide, or very thin noble metal films of gold, silver, copper, and the like, or multi-layered structures comprising these dielectrics and metal films, may be deposited on plastic glazings by such methods. However, it is difficult to prepare metal or dielectric coatings which are uniform across the surface of the glazing by the aforesaid conventional deposition techniques. Due to the difficulties of maintaining uniform consistency, delivery, and distribution of the reactive precursors which form the desired coating at the surface of the glazing substrate, the ultimately produced metal and/or dielectric layer or layers generally exhibit a visually mottled appearance and iridescent patterns.
A publication by R. H. Doremus entitled "Optical Properties of Small Gold Particles", "Journal of Chemical Physics," 40, 2389 (1964), discloses the homogeneous incorporation of gold particles into glass to provide infrared energy reflection while maintaining visible light transmittance. The disclosed method for producing the uniform, homogeneous distribution of gold particles involves adding a gold chloride salt and ceric oxide nucleating agent to a soda-alumina-silica glass melt, irradiating the formed glass with ultraviolet energy, and thereafter heating the glass to a temperature from 400.degree. C. to 630.degree. C. to cause the gold particles to grow homogeneously throughout the glass matrix. Such a structure does not exhibit a mottled appearance or iridescent pattern, as does a glass substrate coated with a thin gold film by the conventional deposition techniques disclosed hereinabove. However, the disclosed structure, having the gold particles dispersed therein, does display infrared reflectance and visible light transmittance comparable to a glass substrate having an adhered gold film. Clearly, the disclosed technique can not be used to form gold particles within a plastic substrate.
It would be desirable to prepare a plastic having uniform infrared reflectance and visual light transmittance, which could be used alone or in association with other transparent materials, to produce enhanced solar control automotive and architectural glazings free from mottling and iridescent patterns.